Within recent years, telephone sets incorporating push-button arrays, commonly including twelve such push-buttons, have come into widespread use and have largely supplanted the previously common rotary dial-type telephone. The individual push-buttons comprising such a telephone set array normally project through the cover of the telephone, or a portion of the telephone cover. The remainder of the switching array is contained beneath this outer shell of the telephone set. Such telephone sets are also employed in coin-operated pay stations which are generally located in high volume traffic areas where they are subject to damage from environmental hazards, incuding especially dust, liquid, and the like which can readily seep through the openings surrounding the individual push-button keys and cause damage, in some cases irreparable damage, to the underlying switching device. In such installations, there is also a great likelihood of damage resulting from vandalism, and a protective cover which is permanently attached, and not easily removed, and yet allowing effective operation of the push-buttons is very desirable.
While several types of covering elements have been previously proposed for use in connection with push-button type telephones, these have not fully addressed the foregoing problem of providing a protective envelopment of the push-button array to prevent damage. For example, patents such as U.S. Pat. Nos. 3,739,105; 3,927,282; 4,002,855; and 3,345,769, have been concerned with a variety of problems including arrangement for facilitating actuation of the buttons by varying spacing of the actuating means for the individual push-buttons, or in the case of U.S. Pat. No. 3,345,769, providing a means for supporing message pads or the like.
In my aforementioned applications a protective covering device is disclosed which provides a flexible sheet or membrane that overlies the pushbuttons. In front of each key this membrane is formed with a thickened region or projection that itself normally bears indicia identifying the particular key. The membrane is continuous, so that it completely seals in the delicate underlying switches.
Such an arrangement has not, however, proven highly vandal resistant. The elastomeric sheet is normally adhesively bonded to the front face of the support plate so that it can be peeled off simply by starting at a corner and working across. This exposes the delicate underlying push-button mechanism, and makes the phone a likely candidate for vandalizing and destruction by the elements.
Another problem with this known arrangement is that the buttons can wear and become illegible. They are mainly made of the same relatively soft material as the seal membrane, so that normal use alone is capable of wearing them down.